Hematology: Normal Hemostasis And Coagulation

Front 1

What is hemostasis?

Back 1

A combination of cellular & biochemical events that function in harmony to 1. keep blood liquid in veins & arteries; 2. prevent blood loss by thrombi formation; & 3. re-establish blood flow during the healing process.

Front 2

Cellular elements of hemostasis.

Back 2

- Vascular intima (blood vessels)
- Blood platelets
- RBCs
- Lymphocytes
- Monocytes

Front 3

Enzyme systems of hemostasis.

Back 3

Coagulation/fibrinolysis mechanisms.

Front 4

Mechanism of primary hemostasis.

Back 4

Activated by small injuries to blood vessels or damage to endothelial cells--> blood vessel contracts to seal the wound and platelet plug formation.

Front 5

Characteristic of primary hemostasis d/o.

Back 5

Mucous membrane hemmorhages.

Front 6

Mechanism of secondary hemostasis.

Back 6

- Is triggered directly or by primary hemostasis & is necessary to control bleeding from large wounds incurred through trauma, surgery, or dental procedures.
- Coagulation cascade resulting in the formation of cross-linked fibrin.

Front 7

Primary procoagulant roles of the blood vessel.

Back 7

Constrict & provide collagen & other compounds to activate clotting.

Front 8

Anticogulant properties if intact endothelium.

Back 8

- Cells are rhomboid, presenting a smooth, contigious surface
- Secretes prostacyclin: plt. activation inhibitor
- Secretes nitric oxide: counteracts vasocnstriction
- Secretes heparan sulfate: slows coagulation by acivating antithrombin.
- Secretes tissue factor pathway inhibitor (TFPI): inactivates coagulation factor VIIa & controls the tissue factor pathway.
- Maintains cell membrane thrombomodulin, protein C coagulation control system activator.

Front 9

Fibrinolytic properties of the vascular intima.

Back 9

Secretes tissue plasminogen activator (TPA) w/c binds fibrin & triggers the activation of plasminogen--> plasmin w/c digests the thrombus & re-stores blood flow.

Front 10

Release process of platelets into peripheral circulation from the bone marrow.

Back 10

Megakaryocytes cytoplasmic fragments extend through the endothelial cells, lining the sinusoids, into blood & then shed platelets.

Front 11

Platelet ultrastructures.

Back 11

- Membrane resembles any biologic membrane; a bilayer composed of proteins & lipids.
- Platelet membrane supports categories of receptors that support the initial phases of plt. adhesion & aggregation.

Front 12

Most important adhesion receptor.

Back 12

GP Ib/IX/V= vWF receptor (CD42)

Front 13

Receptor for fibrinogen.

Back 13

GP IIb & IIIa- "hidden" receptor in resting plt.; required for plt. aggregation.

Front 14

Platelet structural zone.

Back 14

- Consists of microtubules & a network of proteins (maintain plt. shape & contract on activatin to encourage expression of alpha-granule contents)
- Actin is the most abundant protein.

Front 15

Function of platelet granules.

Back 15

Serve as storage sites for proteins & other substances essential for platelet function.

Front 16

Dense bodies (delta granules).

Back 16

Appear more dense in electron microscope preparations- contain mediators of plt. function & hemostasis that are not proteins (ADP, serotonin, ATP, Ca+ & Mg+).

Front 17

Alpha granules.

Back 17

- Most numerous plt. granule contains hemostatic & non-hemostatic proteins.
- Some are synthesized by the plt (vWF & Factor V).
- Others sre absorbed/endocytosed from the plasma (fibrinogen, Ig, albumin)
- Some alpha granule contents are found exclusively in plts (i.e., PF4, PDGF, PAI-1)

Front 18

Function of platelet derived growth factor (PDGF).

Back 18

Stimulates smooth muscle to multiply & replace the damaged cells (allowing the vessel to heal).

Front 19

Primary hemostatic plug.

Back 19

Is the result of the transformation of plts from an inactive (non-adhesive) to an active (adhesive) state.

Front 20

Events involved in the normal formation of primary plug.

Back 20

1. Adhesion
2. Aggregation
3. Granule secretion
4. Secondary hemostasis

Front 21

Platelet adhesion.

Back 21

- 1st step in primary plug formation.
- Attachment of plt. to collagen fibers in subendothelium (directly in low shear stress areas)
- Requires the presence of vWF & the GPIb/IX/V receptor (in high shear stress areas to "carpet" the injury site.
- Does not include the secretion of granules.

Front 22

Agonist.

Back 22

- Substances that stimulate & activate platelets.
- Collagen, Thrombin, ADP, Epinephrine, Thromboxane A2

Front 23

Platelet aggregation.

Back 23

- Attachment of platelets to each other.
- Required the active conformation of the GPIIb/IIIa receptor.
- Part of primary hemostasis (plt-vWF plug)

Front 24

Platelet secretion.

Back 24

- Plt granule content d/c into the surrounding area.
- Requires ATP.
- Delta granules release ADP & Calcium necessary for fibrinogen attachment & secondary hemostasis.
- Release of alpha granules --> secondary hemostasis.

Front 25

Other blood cells role in coagulation.

Back 25

- RBCs: add bulk to fibrin clot.
- Lymphocytes & monocytes: provide tissue factor that triggers coagulation in inflammation.

Front 26

Serine proteases.

Back 26

- Proteolytic enzymes: Factor 2, 7, 9, 10,11, 12, & pre-Kallikrein.
- Function in harmony to form a fibrin clot (secondary hemostasis).
- Absence of a single plasma procoagulant --> lifelong hemorrhage, chronic inflammation, transfusion dependence.

Front 27

Coagulation system.

Back 27

- Activation of procoagulants is localized to the site of the injury.
- Occurs on the surface of the plts/endothelial cell membrane phospholipids (not in fluid phase).

Front 28

Fibrinogen (Factor I).

Back 28

- Ultimate substrate (acted upon by the enzyme thrombin) of the coagulation pathway.
- The only coagulation protein that does not become an activated enzyme.
- Forms the primary structural protein of the fibrin clot.
- Refrence range: 200-400mg/dL

Front 29

Zymogens.

Back 29

Enzymes that circulate in an inactive form.

Front 30

Cofactors.

Back 30

- Bind specific serine proteases--> stability & increased reactivity of enzyme.
- Tissue factor, Factor 5, 8, & high molecular weight kininogen (HMWK).

Front 31

Factor XIIIa.

Back 31

The only coagulation protein w/ transglutaminase activity- form stable, covalent, fibrin cross links.

Front 32

Vitamin K dependent.

Back 32

- Prothrombin (Factor II)
- Factor 7, 9, & 10.
- Regulatory proteins: protein C & S.

Front 33

Vitamin K.

Back 33

- Fat soluble vitamin (quinone) found in green leafy vegetables, fish, liver.
- Synthesized by some Gram negative bacteria.
- Catalyzes glutamic acid--> y-carboxyglutamic acid reaction.

Front 34

Prothrombin group proteins.

Back 34

Essential post-translation modification= glutamic acid--> y-carboxyglutamic acid (critical for calcium binding properties of Prothrombin group proteins)

Front 35

Vitamin K deficiency.

Back 35

- Vitamin K dependent procoagulans released from the liver but unable to participate in coagulation.
- Non-functional; lack COOH group that binda calcium.

Front 36

Vitamin K antagonist.

Back 36

Warfarin/Coumadin (oral anti-coagulant therapy).

Front 37

Fibrinogen group proteins.

Back 37

- Fibrinogen (Factor I), factors V, VIII, & XIII.
- Acted upon by thrombin.
- Have the highest molecular weights of all factors.
- Not found in serum; consumed during clotting.

Front 38

von Willibrand Factor (vWF)

Back 38

- Provides receptor sites for plts (adhesion) & collagen.
- Transports the procoagulant factor VIII.
- Synthesized in megakaryocytes (alpha granules) & endothelial cells.

Front 39

Factor VIII.

Back 39

- Labile deteriorates rapidly; depends on vWF for stability.
- Hemophilia A: decreased factor VIII w/ normal vWF levels.
- von Willebrannd Dz: decreased vWF & factor VIII.

Front 40

Contact factor complex.

Back 40

- Factor XI, XII, high molecular weight kininogen (HK), & prekallikrein (PK).
- Requires a negatively charged surface for activation (glass, kaolin, ellagic acid).
- Does not require calcium.
- Do not appear to play a major role in vivo except factor XI.

Front 41

Factor XI activation pathway.

Back 41

- Activated by thrombin.
- Factor XIa activates fatcor IX--> fibrin stabilization by fatcor XIIIa.
- Essential to normal coagulation.

Front 42

Four coagulation cascade interacting sets of reactions.

Back 42

- Complex formation on phospholipid membranes- coagulation occurs on cell surface membranes.
- Intrinsic pathway
- Extrinsic pathway
- Common pathway

Front 43

Procoaguant complexes assemble on the PL membrane.

Back 43

- First complex (extrinsic Xase)
- Second complex (intrinsic Xase)
- Third complex (prothrombinase)

Front 44

Tissue factor pathway: first complex

Back 44

Membrane receptor for factor VIIIa (in the presence of PL & Ca2+)--> activation of factors 9 & 10.

Front 45

Tissue factor pathway: second complex

Back 45

- Factor IXa binds factor VIIIa on PL surface & also activates factor X.
- Factor Xa binds Va on PL surfaces.

Front 46

Tissue facor pathway: third complex

Back 46

- Factor Xa/Va complex activates prothrombin= thrombin.
- Thrombin leaves fibrinogen--> fibrin monomer--> polymer
- Factor XIIIa stabilized fibrin polymer.

Front 47

Thrombin

Back 47

- Chief protease of coagulation.
- Primary fn.: Cleave fibrinogen molecule--> fibrin monomer.
- Add'l fns.: activates factors V, VIII, XI (amplifies coagulation); activates factor XIII; initiates activation of plts (agonist); activates protein C pathway; activates thrombin activable fibrinolysis inhibitor (TAFI)

Front 48

Tissue factor pathway inhibitor (TFPI).

Back 48

- Regulatory mechanism.
- Factor VIIa/tissue factor (first complex)--> activates factor 9 & 10.
- Factor Xa reacts w/ first complex to bind TFPI--> inactivates factor VIIIa--> short lived factor VIIa/tissue factor complex.

Front 49

Protein C regulatory system.

Back 49

- Thrombin-thrombomodulin complex--> activates protein C system.
- Activated protein C (APC) binds free plasma protein S--> inactivates Va & VIIIa.

Front 50

Protein S.

Back 50

- Binds to & stabilizes APC (cofactor).
- Vitamin K dependent.
- Only free plasma protein S can serve as APC cofactor.

Front 51

Antithrombin.

Back 51

- Serine protease inhibitor.
- Binds & neutralizes thrombin, fatcors IXa, Xa, XIa, & XIIa.
- Requires heparin for effective anticoagulant activity.

Front 52

Other serine protease inhibitors.

Back 52

- Heparin cofactor II
- Alpha2- macroglobulin.

Front 53

Plasminogen

Back 53

- Single chain protein that binds to fibrin during polymerization.
- Converted to plasmin by bound TPA or urokinase.
- Also binds plasma alpha2-antiplasmin, w/c rapidly & irreversibly binds & inactivates free plasmin (prevents systemic activity).

Front 54

Plasmin

Back 54

- Serine protease that systematically digests the fibrin polymer.
- Capable of digesting fibrinogen & fatcors V & VIII (known as primary fibrinolysis).

Front 55

Fibrinolysis.

Back 55

- Final stage of hemostasis; begins few hours after fibrin polymerization.
- Function: reduce thrombus/clot & re-stre normal blood flow during vascular repair.
- TPA binds to fibrin--> activates plasminogen forming plasmin--> plasmin systematically degrades the fibrin clot into fragments (fibrin degradation product).

Front 56

Tissue Plasminogen Activator (TPA)

Back 56

- Binds to fibrin during polymerization.
- Initiates fibrinolysis by convering plasminogen--> plasmin.
- Free TPA circulates bound to inhibitor & cleared from plasma by the liver.
- Lyses the clot rather than prevents future clots.
- Synthetic TPA used clinically to dissolve clots/thrombi in stroke pts.

Front 57

Urokinase

Back 57

- Plasminogen activator
- Binds to fibrin during polymerization but does not bind firmly like TPA--> relatively minor physiologic effect.

Front 58

Plasminogen Activator Inhibitor-1 (PAI-1)

Back 58

- Fibrinolysis inhibitor
- Prevents activation of TPA & urokinase.

Front 59

Thrombin Activable Fibrinolysis Inhibitor (TAFI)

Back 59

- Activated by the thrombin-thrombomodulin complex.
- Prevents the binding of TPA & plasminogen to fibrin.
- Link between coagulation & fibrinolysis.
- Decrease thrombin production reduces activation of TAFI-->
- Increase thrombin generation increases the activation of TAFI-->

Front 60

Fibrin Degradation Products.

Back 60

- Inhibits hemostasis by preventing plt activation (primary) & fibrin polymerization (secondary).

Front 61

D-dimer (D-D fragment)

Back 61

- A specific marker for thrombosis.
- Used to identify DIC.
- Also used to rule out venous thromboembolism: deep vein thrombosis (DVT) & pulmonary embolism (PE).

Front 62

Unique to the intrinsic pathway

Back 62

Factors 12, 11, 9, & 8

Front 63

Unique to the extrinsic pathway

Back 63

Tissue factor & factor 7

Front 64

Coagulation factors consumed during clotting

Back 64

Fatcors 1, 3, 5, 8, & 13

Front 65

Factors in Common Pathway

Back 65

Factors 10, 5, 2, & 1